Great question and discussion.
My opinion is that you should stay as much as possible with the standards. Since these are platform supported and with conversions to newer versions of Mendix, you can relpy on Mendix. Thats the whole idea behind a low-code platform.
Although you can certainly extend the capabilities of Mendix with your own react widgets. But only when
Above count for use of custom Java as well.
Not because the developer wants to show off its own capabilities by making unmaintainable fancy pancy shizzle.
Rene has already eloquently stated the right approach to React widgets versus Mendix UI elements. So, having that in mind, the main use case for a React widget is when Mendix has no option to implement one of your user’s wishes. For instance, they want to be able to play Tetris incorporated in their Mendix app and store the top-scores in the Mendix database. You want a live example: https://service.mendixcloud.com/p/game/tetris.
just leave this here ;-)